U.S. Pat. No. 4,107,204 provides a three step process for the oxidation of propylene to acrylic acid in the presence of a palladium catalyst and acetic acid. The catalyst employed is a supported palladium-copper or palladium-silver two metal compound.
U.K. Pat. No. 1,433,168, owned by the Assignee of record, is directed toward a one step process for the preparation of acrylate and methacrylate esters from unsaturated aldehydes over known catalysts comprising molybdenum, vanadium and tungsten. The feature of the invention is the addition of alcohol directly to the oxidation reaction, so that it is present with at least some of the aldehyde.
British Pat. No. 2,051,056 discloses a method for preparing carboxylic esters by reacting an aldehyde with an alcohol in the presence of a catalyst comprising palladium and bismuth and optionally an alkali metal or alkaline earth metal or other metal. The catalyst is prepared by chemically reducing a soluble palladium salt to palladium metal while the bismuth is present either in a metallic state or as a bismuth compound such that the two components interact with each other.
The foregoing methods, although relevant to the process of the present invention, would not lead one skilled in that art to the process of this invention, which employs specific palladium based catalysts, and the significant advantages resulting from the practice thereof.